You know the idea of a sound-check; turn up a bit early - test the piano, say 'one, two' quite a lot into the microphones and work on the levels. Time-consuming, tedious, but part of the job. And not usually life-threatening.
At a gig last night where we discovered during the sound-check that the microphones carried a significant electrical charge. So much so that getting within a centimetre of the mic resulted in a little blue cunty arc of electricity firing into my lip.
This quirk was unfortunately uncorrectable prior to the gig, so our swearing during the performance was more frequent, less predictable and much more heart-felt than ever. Bzzzzt - FUCK!